Fluid storage and dispensing vessels are used in a wide variety of industrial, commercial, and personal applications, including, but not limited to, semiconductor fabrication, biomedical and pharmaceutical processes, and many other fields requiring supply of high purity fluids. Various types of liquids, gases, and solid-liquid slurries may be supplied from these vessels, e.g., pressure-rated stainless steel storage cylinders.
Pressure-rated stainless steel containers have many known disadvantages, such as in applications involving storage and dispensing of certain high-purity fluids utilized in the semiconductor industry. Stainless steel is reactive with various fluids. Stainless steel vessels are also not readily disposable. Further, stainless steel vessels are not generally recyclable without return of used vessels to the original equipment manufacturer (OEM) or supplier.
FIG. 2A is a flow chart that shows a conventional supply loop sequence of canisters that are employed in the semiconductor industry. The sequence of processing steps may include filling of a canister with fluid, packaging of the canister, shipment of the canister to a customer, use of the canister by the customer, shipment of the canister to the supplier (denoted ATMI, for example), arrival of the canister in the factory of the supplier, removal of residual chemistry from the vessel, cleaning of the canister, rebuilding and installation of the valve assembly, and refilling and packaging of the canister.
Such cycle involving return of fluid-depleted vessels to the supplier results in expensive refurbishment, cleaning, and component replacement, as is reflected by the chart of FIG. 2B, in which the costs associated with the process loop of FIG. 2A are broken down by cost components, including, in sequence from top to bottom of the three-dimensional column shown in FIG. 2B, shipping cost from the customer, shipping cost to the customer, packaging cost, cost to fill, cost to rebuild valves, cost to clean, cost to remove residual chemistry, and amortized canister cost. The estimated cost of one pressure-rated stainless steel canister making a full cycle in the supply loop shown in FIG. 2A is approximately $700, wherein the estimated cost components of the loop without the canister is approximately $325.
Despite these various costs, and the disadvantages of using stainless steel for fluid supply operations in the semiconductor industry, pressure-rated stainless steel vessels are typically selected for service in semiconductor manufacturing operations, however, due to their pressure ratings and cleanliness specifications.
A substantial number of fluid delivery systems in semiconductor manufacturing applications use a pressure differential to transfer fluids through a dip tube in a bulk canister to a process canister, with the process canister generally being maintained at a constant pressure for uninterrupted supply of fluid. One problem with this design is the requirement that the pressure in the bulk canister must be elevated above the pressure in the process canister in order to effect delivery of liquid into the process canister. As such, these systems generally require the bulk canister to be a pressure-rated stainless steel vessel that is costly to produce (e.g., involving a manufacturing cost on the order of $2,000-$5,000), as well as costly to service and transport, in addition to the stainless steel material construction being reactive with various fluids commonly used in semiconductor manufacturing operations.
A standard pressure level such as 30 psi (206.84 kPa) within the process canister is commonly employed for delivery of fluid in semiconductor manufacturing operations, but the pressure in specific applications may be higher depending on distance between the supply vessel and the semiconductor processing tool, and fluid pressure requirements at the semiconductor processing tool. A bulk canister typically must be at least 5 psi (34.5 kPa) higher than the process canister to ensure efficient transfer of the fluid into the pressurized process canister. Such pressures are increased for fab-wide distribution systems supplying chemicals from a single central bulk delivery system.
High pressure gas in the bulk canister (and other canisters of the process system) will over time, however, result in gas being dissolved in the dispensed fluid (i.e., gas entrainment will occur). Such occurrence in turn necessitates the provision of a degasser downstream from the fluid delivery system to remove the entrained gas. Degassers, however, are not always 100% effective. Moreover, as a majority of fluid is dispensed from the canister, the remaining fluid tends to contain a greater concentration of entrained gas, with the result that the residual fluid usually is discarded. Such discarded volume may be as much as 10% or more of the original fluid charge in the vessel. Given that most semiconductor fluids are very expensive, any waste of fluid is problematic.
FIG. 3 shows a conventional fluid delivery system 300 including a bulk canister 301 and a process canister 302 that are interconnected in fluid flow relationship with one another, with each having associated pressurizing and dispensing lines, arranged so that the fluid flows through the connecting line, from the bulk canister 301 to the process canister 302 in the direction indicated by arrow 305. In this conventional system, the bulk canister 301 is pressurized to a pressure level that is greater than that of the process canister 302. The process canister 302 is arranged to supply fluid to a location of use (e.g., a semiconductor manufacturing tool, not shown in FIG. 3)). Each of the inlet flow circuits to the respective bulk and process canisters includes a pressurizing gas line and a vacuum line. The pressurizing gas line may be coupled to a source of pressurizing gas, such as an inert gas, e.g., helium, argon, nitrogen, etc.
In canisters of the type illustratively shown in FIG. 3, measurement of fluid remaining in the canisters is often accommodated by the provision of float sensors in such vessels. Float sensors, however, are costly and have a history of failure.
In consequence, the art continues to seek improvements in fluid delivery systems and methods. Specific objectives include simplification of the fluid delivery system, reduction of cost of bulk containers, and elimination or reduction of fluid losses due to gas entrainment.